1. Field of the Invention
The present invention relates to a balancer for use in a conveyor apparatus, a machining apparatus, or the like which is displaceable vertically, for pneumatically or hydraulically applying forces against a downward load imposed by a large weight of the apparatus itself or a workpiece supported thereby to reduce the burden on a power source of the apparatus.
2. Description of the Related Art
Cylinders have heretofore been used in certain applications for conveying heavy workpieces substantially upwardly. To position a workpiece in a vertical direction with a cylinder, a pressure fluid control valve or the like is operated to equalize a primary pressure supplied to the cylinder and a secondary pressure discharged from the cylinder for thereby holding the cylinder in a corresponding operative position.
However, since the workpiece is positioned with a cylinder using a fluid under pressure, the response speed is low. In addition, when the primary pressure supplied to the cylinder fluctuates, it is not possible to position the workpiece accurately.
In view of the above problems, it has been customary to employ a balancer composed of a cylinder and an actuator which comprises an electric motor for rotating a ball screw that functions as a drive force transmitting shaft. The balancer can convey a heavy workpiece upwardly by lessening, with the cylinder, any excessive burden that is applied to the electric motor by the weight of the workpiece. The balancer is capable of positioning the workpiece highly accurately by introducing a signal from a detector such as an encoder as being indicative of the rotational speed of the electric motor.
The actuator and the cylinder, which are separate members, are coupled to each other. The cylinder is exposed from the body of the actuator, and requires an additional space for installation. When the ball screw is rotated by the electric motor, a table mechanism is displaced to move the workpiece supported thereon. The table mechanism needs to be connected to the piston rod of the cylinder by a certain mechanism. Consequently, the number of parts of the conventional balancer is relatively large.